--- a/PresetMaps.wiki	Tue May 02 17:36:48 2017 +0100
+++ b/PresetMaps.wiki	Fri May 05 21:29:02 2017 +0100
@@ -57,6 +57,7 @@
 
 ==== `map.png` ====
 Image of visible land area.
+  * 32-bit PNG with alpha channel
   * Usually _width/length ratio_ of 2:1
   * Typical size: 2048 x 1024
   * Max size: no limit, 0.9.18+.  4096 x 2048 or less in 0.9.17 and earlier.  There are a few practical limits to map size that should be examined for people trying to make very large maps.